Showing papers in "Journal of Microwave Power and Electromagnetic Energy in 1996"
TL;DR: In this paper, a theoretical analysis of athermal, specific or molecular effects of microwave heating claimed in chemistry is presented. But this analysis is restricted to a single class of effects: biological effects of electromagnetic irradiation.
Abstract: The purpose of this paper is to enlighten by a theoretical analysis the controversial question of athermal, specific or molecular effects of microwave heating claimed in chemistry.In this Part 1, thermodynamic considerations relating to transition state theories are reviewed. The different assumption.s of specific effects claimed in chemistry are examined, and a brief overview of biological effects of electromagnetic irradiation are reported. Chemical experiments which claim athermal effects then are analyzed. Finally, fundamentals of wave matter interaction are given.
132 citations
TL;DR: In this article, the authors formulated six criteria relating to the existence of microwave athermal effects and formulated these criteria leading to the formulation of a general theorem relating to existence of molecular effects in micro valve heating.
Abstract: The purpose of this paper is to enlighten by a theoretical analysis the controversial question of atnermul, specific or molecular effects of microwave heating claimed in chemistry.In this Part II, orienting effects of electric field, and physical origin of dielectric loss will be analyzed, as well as transfers between rotational states and vibrational states within condensed phases. We will formulate six criteria relating to existence of microwave athermal effects. In fact these criteria will look like some lemma leading then to the formulation of a general theorem relating to existence of molecular or athermal effects in micro valve heating. In the usual operating conditions, it will be proven that the frequently propounded idea that the microwaves rotate dipolar groups is misleading.
87 citations
TL;DR: In this article, the requirements for a free space microwave transmission measurernent system for determining the permittivity of grain are analyzed and experimental verification of these requirements is provided for two cultivars of hard red winter wheat of various densities, moisture contents and temperatures in the frequency range from 10 to 18 GHz.
Abstract: Requirements for a free space microwave transmission measurernent system for determining the permittivity of grain are analyzed. Experimental verification of these requirements is providedfor two cultivars ofhard red winter wheat of various densities, moisture contents and temperatures in the frequency range from 10 to 18 GHz. Uncertainties in the dielectric constant determination are less than ±1%, and those for the loss factor are less than ,±.3%.
62 citations
TL;DR: In this article, the electromagnetic fields and power distribution in the polymer material within the waveguide are predicted by means of the finite-difference time-domain (FD-TD) technique.
Abstract: Microwave joining of polymer materials using ridge waveguides is a relatively new area of research. In order to gain insight into the phenomena that occur inside the ridge waveguide, together with the temperature distribution in the polymer material, a detailed knowledge of the power distribution is necessary. In this paper, Maxwell’s electromagnetic equations are coupled to the heat transfer equation and solved numerically in order to simulate the microwave heating of a polymer material inside a ridge waveguide. The electromagnetic. fields and power distribution in the polymer material within the waveguide are predicted by means of the finite-difference time-domain (FD-TD) technique. The FD-TD scheme is modified for the field component adjacent to the curved surface of the ridge waveguide by applying the contour path technique.
41 citations
TL;DR: In this paper, an investigation of the microwave heating of a lossy material located inside a cavity by the Finite-Difference Time Domain (FD-TD) method is undertaken, where the authors focus on the performance of the FD-TD method when certain traditional assumptions are used within the framework of the model.
Abstract: In this paper, an investigation of the microwave heating of a lossy material located inside a cavity by the Finite-Difference Time-Domain (FD-TD) method is undertaken. The emphasis of this work focuses on the performance of the FD-TD method when certain traditional assumptions are used within the framework of the model. The limitations of these assumptions will be deliberated and more accurate counterparts will be proposed and tested. In particular, it will be shown that when only a single mode is assumed to exist around the aperture between the wave guide and the cavity, spurious numerical resiilts arise. Further, the numerical simulation indicates that the treatment of the interfacial boundary condition located between free-space and the material becomes very important when predicting the dissipated power distribution for a lossy dielectric material. A new approximation of this interfacial boundary condition is developed and a comparison between existing and new methodologies is made. The treatment of s...
35 citations
TL;DR: In this article, the shape-and size-independent measurements are discussed, and experimental results for moisture content and mass measurement of individual soybeans, peanuts and grain kernels, as well as for mass determinations on irregularly shaped objects of common plastic materials are presented.
Abstract: Microwave resonators have been used as sensors for determining material properties of dielectric objects, including permittivity, density, moisture content, and mass, from measurements of frequency shift and change in cavity transmission characteristics when a small dielectric object is inserted into a microwave resonant cavity. Fundamental principles of the shape-and size-independent measurements are discussed, and experimental results for moisture content and mass measurement of individual soybeans, peanuts and grain kernels, as well as for mass determinations on irregularly shaped objects of common plastic materials are presented. Measurements are fast, nondestructive, contactless, and have the potential for continuous operation.
32 citations
TL;DR: In this paper, the authors estimate the dielectric constants of coal and limestone at 11.7 GHz and 20°C from measurements of the permittivities and bulk densities of pulverized samples and the particle material density.
Abstract: Estimates for the permittivities of solid coal and limestone at 11.7 GHz and 20°C are obtained from measurements of the permittivities and bulk densities of pulverized samples and the particle material density. Linear regressions of the cube root of the dielectric constant on sample bulk density provide estimates of the dielectric constants of the solid materials. Since linearity with bulk density of the cube root of the dielectric constant is consistent with the Landau & Lifshitz, Looyenga dielectric mixture equation, that equation provides estimates for both the dielectric constant and loss factor when the relative complex permittivities are used for the calculation.
31 citations
TL;DR: In this article, the Finite Difference Time Domain (FDTD) method is applied to industrial microwave ovens used in the food industry and theoretical and practical aspects of FDTD analysis for this purpose are dealt with.
Abstract: The Finite Difference Time Domain (FDTD) method is applied to industrial microwave ovens used in the food industry. Theoretical and practical aspects of FDTD analysis for this purpose are dealt wit...
31 citations
TL;DR: An original microwave-ultrasound combined reactor has been developed as discussed by the authors for organic synthesis and its application to organic synthesis has been shown by two examples of chemical reactions where increases in yield were demonstrated: pyrolysis and esterification.
Abstract: An original microwave-ultrasound combined reactor has been developed. Its application to organic synthesis has been shown by two examples of chemical reactions where increases in yield were demonstrated: pyrolysis and esterification.
31 citations
TL;DR: In this article, the dielectric properties of four native starch solutions, both gelatinized and ungelatinized with concentrations from 5 to 30% over the temperature range from 3°C to 95°C, were measured by a cavity perturbation technique at 175 GHz.
Abstract: The dielectric properties of four native starch solutions, both gelatinized and ungelatinized with concentrations from 5 to 30% over the temperature range from 3°C to 95°C, were measured by a cavity perturbation technique at 175 GHz. The dielectric properties of the starch types did not differ from each other; the most important factor affecting the dielectric properties was the water content. Both the real permittivity (e’) and the loss factor (e”) decreased with increasing temperature and increasing starch concentration. The differences between gelatinized and non gelatinized samples were small, the e’” of non gelatinized starch being 2–3% higher and the e up to 5% lower than gelatinized starch.
29 citations
TL;DR: In this paper, the authors present an overview of the measurement systems and measurements on an alumina/zirconia system, showing agreement between the results obtained by both techniques.
Abstract: The application of microwave energy to the processing of ceramic materials is a promising technology of wide interest, although it still holds some technical challenges. Complex permittivities of many ceramic materials often exhibit significant temperature dependence and influence the volumetric heating behavior of these materials when exposed to microwave radiation. Two techniques have been developed to obtain permittivity measurements up to about 1200°C. These systems have been fully automated, providing results in real time. This paper presents an overview of the measurement systems and measurements on an alumina/zirconia system, showing agreement between the results obtained by both techniques.
TL;DR: A circuit model of a class C radio frequency industrial system has been developed using a novel method based on non-linear optimization to determine the tank circuit parameters together with its mutual coupling to the applicator.
Abstract: A circuit model of a class C radio frequency industrial system has been developed. A novel method based on non-linear optimization is used to determine the tank circuit parameters together with its mutual coupling to the applicator. A model is also derived for the triode valve using the manufacturer’s data. The actual parameters of a 13.56 MHz radio frequency system are measured and used in the electrical model in order to enable their comparison. The model is then analyzed in the time-domain using the Saber circuit simulator. The results obtained from the model show good agreement with experiments.
TL;DR: In this article, the authors used the finite difference time domain (FDTD) method to derive electromagnetic field distributions in a mass-produced microwave oven where the particular influence of the magnetron output antenna in a short feeding wave guide was considered or not considered.
Abstract: The finite-difference time-domain (FDTD) method was used to derive electromagnetic field distributions in a mass-produced microwave oven where the particular influence of the magnetron output antenna in a short feeding wave guide was considered or not considered It was confirmed in visual and quantitative comparison that the influence of the magnetron antenna geometry is negligible. A procedure for reduction of uneven heating is also discussed, using an approach of oven development as a practical example.
TL;DR: This paper will employ the finite difference time domain method to study three major types of microwave heating applicators and thereby demonstrate the capabilities of this technique to analyze a variety of microwave cooling applicators.
Abstract: Microwave heating plays a significant role in the processing of materials in industry, but the applicator design is generally done without numerical methods or simulations because of the difficulty of the design problem. Much research has shown that the finite difference time domain method can model complex geometries and analyze many types of electromagnetic problems. This paper will employ this approach to study three major types of microwave heating applicators and thereby demonstrate the capabilities of this technique to analyze a variety of microwave heating applicators.
TL;DR: A variety of microwave applicators were designed, fabricated and tested for catheter applications, and most radiators designed produced larger lesions than have been described previously.
Abstract: A variety of microwave applicators were designed, fabricated and tested for catheter applications: I-radiators, U-radiators, O-radiators, forward helical coil radiator, reverse helical coil, double coil radiator, loaded monopole radiator, leaky coaxial radiator and tee radiators. The comparative and relative radiation characteristics of these applicators were tested in a saline bath and tissues. Most radiators designed produced larger lesions than have been described previously.
TL;DR: In this article, the feasibility of microwave sintering of BaTiO3-based ceramics was examined and the conditions for a homogeneous Sintering for microwave heated samples were ascertained.
Abstract: The feasibility of microwave sintering of BaTiO3-based ceramics was examined and the conditions for a homogeneous sintering for microwave heated samples were ascertained.A comparative study of microwave sintering and conventional sintering was undertaken to determine differences in shrinkage behavior and microstructure development. All microwave sintered ceramics showed an enhanced shrinkage during the solid state sintering stage and in particular in the case of Cu-doped samples (secondary phase promoted microwave sintering) a lowering in sintering temperature was observed.
TL;DR: In this article, a new procedure for monitoring dielectric permittivities at microwave frequencies is presented, which exploits an extension of the Cavity Perturbation Method (CPM).
Abstract: A new procedure for monitoring dielectric permittivities at microwave frequencies is presented. It exploits an extension of the Cavity Perturbation Method The core of this procedure consists in the analysis of the power reflected by a cavity at resonance by means of quick and narrow frequency sweeps which can be rapidly and smartly updated in order to track the resonance. The new method has been tested with an experimental setup herewith described. Some experiments have been addressed on samples undergoing chemical (polymerization) and physical (vaporization) changes and their results are also reported. The method can be implemented by the use of commercial devices and it can be easily automated for supporting field applications.
TL;DR: In this paper, a model that predicts the microwave heating behavior of granular hygroscopic solids with low spatial dimension-topenetration depth ratio was derived, consisting of an energy transport equation based on a macroscopic application of the energy conservation, the series solution of Fick's diffusion equation, and a modified Gallaher's equation.
Abstract: A model that predicts the microwave heating behavior of granular hygroscopic solids with low spatial dimension-topenetration depth ratio was derived. The model consists of an energy transport equation based on a macroscopic application of the law of energy conservation, the series solution of Fick’s diffusion equation, and a modified Gallaher’s equation. The model gave a good prediction of the microwave heating characteristics of white beans. A sensitivity analysis of the model indicates that the microwave heating characteristics of a moist hygroscopic dielectric is sensitive to initial moisture content, size and heat transfer coefficient.
TL;DR: In this article, a graphical view of modes in an empty rectangular microwave cavity through finite element modelling is presented, which leads to perspectives on cross-coupling in multiple-feed cavities.
Abstract: A graphical view of modes in an empty rectangular microwave cavity through finite element modelling are presented. This leads to perspectives on cross-coupling in multiple-feed cavities. The construction of a cavity and the positioning of feeds for reduced cross coupling through an understanding of magnetic and electric field distributions, is discussed The limitation of the present analysis is that it applies to an empty cavity; however, useful insights can be derived.
TL;DR: The review indicates that the microwave auditory effect is the only well-established specific effect in realistic exposure situations and energy density limits have been included in the most recent exposure standards.
Abstract: Observed biological effects of pulsed microwave radiation are reviewed and the exposure standards for microwave radiation are summarized. The review indicates that the microwave auditory effect is the only well-established specific effect in realistic exposure situations. The threshold for the effect depends on the energy density per pulse and may be as low as 20 mJ/m2 for people with low hearing threshold. Energy density limits have been included in the most recent exposure standards. A new battery-operated, hand-held meter developed for measurements of pulse power densities around scanning radar antennas is described, and a simple new model for the calculation of power density in the main beam of radar antennas is presented. In the near field measured values differed from the calculated values by 2-3 dB.
TL;DR: In this article, the cabbage maggot (Delia radicum) [Diptera: Anthornyiidae] was treated in an industrial microwave oven (f = 2450 MHz; P =0 to 6 kW) to test two developmental stages of the insect.
Abstract: To control the cabbage maggot (Delia radicum) [Diptera: Anthornyiidae], treatments in an industrial microwave oven (f = 2450 MHz; P =0 to 6 kW)were carried out in the laboratory to test two developmental stages of the insect. First, treatments were directed at Delia radicum eggs after the transplanting of cabbage plants. Treatments with 10 sat 2100 W, 20 s at 1600 W, 20 s at 2100 W, 25 s at 1100 W, 25 s at 1600 W and 25 s at 2100 W inhibited egg hatching. However, exposures caused lethal effects in cabbage plants (Brassica oleracea var. Swnehead). Second, treatments were directed at the maggot pupae after harvest. Treatments with 10 s at 3000 Wand 10 s at 4000 W were more promising, inhibiting the emergence of adults while having no impact on the cabbage plant. Post-harvest treatment would be preferable to spring treatment. High energy levels required to penetrate the soil at a depth of 10 cm to attain all pupae preclude commercial development at the present time.
TL;DR: In this article, the first attempt was made in microstrip technology at a frequency of 10 GHz, which is the same as the one we use in our measurement cell and is based on a complex correlator associated with a measurement cell.
Abstract: The progress in microwave technology allows one to think that original and low cost sensors for various applications may be feasible. In this paper a sensor devoted to the characterization of material webs is presented. This sensor is based on the use of a complex correlator associated with a measurement cell. The first attempt was made in microstrip technology at a frequency of 10 GHz.
TL;DR: In this paper, the identification of resonant modes in a rectangular cavity loaded with homogeneous dielectric layers was investigated, and computer programs were developed based on an approach that leads to a unique mode identification.
Abstract: In this paper identification of resonant modes in a rectangular cavity loaded with homogeneous dielectric layers was investigated. Computer programs were developed based on an approach that leads to a unique mode identification. Characteristic examples of mode identification are given.
TL;DR: In this paper, the feasibility of ice presence detection and ice thickness monitoring, based on measurements of the amplitude of the reflection coefficient at microwave frequencies, is discussed, and theoretical calculations and experimental evaluations of the performance of microstrip sensors are presented.
Abstract: The feasibility of ice presence detection and ice thickness monitoring, based on measurements of the amplitude of the reflection coefficient at microwave frequencies, is discussed. Also, theoretical calculations and experimental evaluations of the performance of microstrip sensors are presented.
TL;DR: In this paper, the advantages of the RF technique over microwave technology are discussed, and the disadvantages of using microwave technology over RF technology over high-power pulse radio-frequency irradiation are discussed.
Abstract: Decomposition (extraction) of metal-containing ore samples mixed with a carbon source has been achieved by high-power pulse radio-frequency irradiation. Elimination of electrical discharges, which have been an inherent problem in other high-power microwave studies, can be accomplished by careful manipulation of the pulse characteristics. The advantages of the RF technique over microwave technology are discussed.
TL;DR: The heat of desorption characteristics of moisture in hygroscopic solid dielectrics during microwave drying was investigated in this article, where white bean seeds were used as the experimental material.
Abstract: The heat of desorption characteristics of moisture in hygroscopic solid dielectrics during microwave drying was investigated. White bean seeds were used as the experimental material. A direct method for determining the heat of desorption of moisture was developed. Results indicate that the heat of desorption offree water during microwave heating is lower than that during conventional heating. However, the heat of desorption of bound water during microwave drying was above that for conventional drying. This indicates that polarization of solid dielectrics may induce additional binding forces for bound moisture thus increasing the heat of desorption. The implication of this is that microwave drying of solids that do not become polarized is likely to be more energy efficient than those that become polarized in the microwave field. The lower the level of polarization ofa solid, the greater the microwave drying efficiency and effectiveness.
TL;DR: In this article, basic structural investigations on rape-seed as an example of a natural granular material with spherical shape are presented, which relates dielectric constant, moisture content and structure coefficients.
Abstract: Basic structural investigations on rape-seed as an example of a natural granular material with spherical shape are presented. Moisture dependent structure coefficients such as bulk and kernel density were measured in an especially developed apparatus. It was found, that density independence of a microwave moisture measurement could be obtained by applying a properly defined pre-pressure to a layer of material, thus obtaining moisture independent porosity and density. Furthermore, a permittivity model for rape-seed is presented, which relates dielectric constant, moisture content and structure coefficients. The various binding states ofwater as well as moisture dependent swelling of the seeds are included. The permittivity model was substantiated by dielectric measurements in X-band.
TL;DR: In this article, a microwave free-space method based on two-polarized forward scattering is used to measure the average volume of the inclusions of a granular material in the Rayleigh region.
Abstract: Limitations of a microwave free-space method based on two-polarized forward scattering are discussed. The method can be used e.g. to measure the average volume of the inclusions of a granular material in the Rayleigh-region. The minimum and the maximum thicknesses of the measured material are determined by the complex permittivity, the shape and the number density of the inclusions of the material, the measurement frequency and the properties of the measurement equipment. Theoretical background of the method is presented. The measurable thickness range of several common granular materials with typical properties, calculated on the basis of the theory have been tabulated.